1. Field of the Invention
The present invention relates to a fuel injector for internal combustion engines.
2. Background Information
Fuel injectors are used to introduce pressurized fuel into the combustion chamber of an internal combustion engine. FIG. 1 shows a fuel injection system 10 of the prior art. The injection system includes a nozzle 12 that communicates with a fuel inlet port 14 through an intensifier chamber 16. The intensifier chamber 16 contains an intensifier piston 18 which reduces the volume of the chamber 16 and increases the pressure of the fuel therein. The pressurized fuel is released into a combustion chamber of an engine through the nozzle 12.
The intensifier piston 18 is moved by a working fluid that is controlled by a poppet valve 20. The working fluid enters the fuel injector through inlet port 22. The poppet valve 20 is coupled to a solenoid 24 which can be selectively energized to pull the valve 20 into an open position. As shown in FIG. 2, when the solenoid 24 opens the poppet valve 20, the working fluid applies a pressure to the intensifier piston 18. The pressure of the working fluid moves the piston 18 and pressurizes the fuel. When the solenoid 24 is de-energized, mechanical springs 26 and 28 return the poppet valve 20 and the intensifier piston 18 back to their original positions. Spring 30 returns a needle valve 32 to a closed position to close the nozzle 12.
Fuel injectors having mechanical return springs are relatively slow because of the slow response time of the return springs. Additionally, the spring rate of the poppet spring generates an additional force which must be overcome by the solenoid. Consequently the solenoid must be provided with enough current to overcome the spring force and the inertia of the valve. Higher currents generate additional heat which degrades the life and performance of the solenoid. Furthermore, the spring rate of the springs may change over time because of creep and fatigue. The change in spring rate will create varying results over the life of the injector. It would be desirable to provide a fuel injector which does not have any mechanical return springs.